(CNN) — At least 51 people — including at least 20 children — were killed when a massive tornado struck an area outside Oklahoma City on Monday afternoon, officials said.

Seven of those children were killed at Plaza Towers Elementary School in Moore, Oklahoma, according to a police official.

Early Tuesday, emergency personnel continued to scour the school’s rubble — a scene of twisted I-beams and crumbled cinder blocks.

The tornado was estimated to be at least two miles wide at one point as it moved through Moore, in the southern part of the Oklahoma City metropolitan area, KFOR reported. Video from CNN affiliates showed a funnel cloud stretching from the sky to the ground, kicking up debris.

Latest updates:

– Some of the children killed at Plaza Towers Elementary School in Moore, Oklahoma, during Monday’s storm drowned in a basement area there, Oklahoma Lt. Gov. Todd Lamb told CNN Tuesday morning. “My understanding, this school … Plaza Towers, they had a basement. Quite frankly, don’t mean to be graphic, but that’s why some of the children drowned, because they were in the basement area,” he said. Officials have said the storm killed at least seven children at the school.

– Queen Elizabeth II sent her condolences to those affected by Monday’s massive deadly Oklahoma tornado, saying on Twitter: “Our deepest sympathies go out to all those whose lives have been affected, as well as the American people #Oklahoma #tornado.”

Previously reported:

– Pope Francis urged people to join him in praying for the families of those who died in the massive tornado in central Oklahoma on Monday, “especially those who lost young children,” he said in a tweet Tuesday.

– President Barack Obama will make a statement at approximately 10 a.m. ET after he is briefed on the aftermath of the Oklahoma tornado devastation, a White House official told CNN. The statement will be delivered in the State Dining Room.

– French President Francois Hollande expressed his grief over the casualties caused by the ferocious Oklahoma tornado and saluted the “mobilization” of citizens who tackled “this exceptional situation with courage and determination.”

– German Chancellor Angela Merkel passed along her condolences to President Obama over the casualties and destruction caused by the mammoth tornado that tore through Oklahoma on Monday. “The pictures of this catastrophe render us speechless and can only hint at the scope of the hurt,” Merkel told the president Tuesday.

– The Oklahoma Medical Examiner’s Office has been told to expect about 40 additional bodies, including about 20 children, according spokeswoman Amy Elliott. The official death toll of 51 will not rise until the bodies are processed, she said. The current toll already includes at least 20 children who were killed by the storm.

– At least 145 people have been hospitalized in the Oklahoma City, hospital officials said.

– The Children’s Hospital at OU Medical Center received 45 children for treatment on Monday, according Dr. Roxie Albrecht.

– The threat of severe weather shifts to the southeast on Tuesday, covering parts of north Texas, southwest Arkansas and northwest Louisiana, the National Weather Service said.

–The city of Moore, Oklahoma, has no running water, Mayor Glenn Lewis told CNN on Monday evening. It was uncertain when water service would be restored.

– Texas is sending the state’s elite search and rescue team, Texas Task Force 1, to assist local officials and first responders in Oklahoma following Monday’s tornado outbreak.

– Obama signed a disaster declaration for Oklahoma on Monday night, a White House statement said. The declaration means federal emergency aid will supplement local recovery efforts.

– Storm damage has been reported in Cleveland County, which includes Moore; McClain County, which includes Newcastle; and Oklahoma County, Oklahoma Department of Emergency Management representative Terri Watkins said.

– The preliminary rating of the Moore tornado is at least EF4 (166 to 200 mph), the National Weather Service said on Monday afternoon.

– Obama told Oklahoma Gov. Mary Fallin that the federal government “stands ready to provide all available assistance” as part of the response to a series of deadly storms that have struck the Oklahoma City area, including Monday’s devastating tornado.

A White House statement said the Federal Emergency Management Agency has deployed a team to assist state operations, and additional personnel are ready to be dispatched as necessary. Obama told Fallin that “the people of Oklahoma” are in the first family’s “thoughts and prayers,” the statement said.

– About 38,000 customers of utility OG&E were without power in metropolitan Oklahoma City after Monday afternoon’s storm, utility spokesman Brian Alford said.

Alford also said the storm knocked out power to the Oklahoma City area’s Draper Water Treatment Plant.

OG&E is working to restore power to the plant. City officials are asking residents to turn off their sprinkler systems and postpone washing dishes and clothes, according to a message on the city government’s website.

– Country music star and Moore native Toby Keith said in a written statement: “This storm has devastated the community that I grew up in. I rode my bike through those neighborhoods. I have family and friends in Moore. My heart and prayers go to those that have lost so much. But Moore is strong and we will persevere. God be with you all.”

– Interstate 35 in Moore was closed as a result of debris from the tornado that hit the area Monday afternoon, Oklahoma Department of Transportation spokesman Cole Hackett said. Crews were headed to the north-south highway to start the cleanup process, Hackett said.

– “People are trapped. You are going to see the devastation for days to come,” Betsy Randolph, a spokeswoman for the Oklahoma Highway Patrol, told CNN late Monday afternoon. She did not say how many people were trapped. “Send your prayers heavenward because there are people fighting for their lives.”

– The National Guard has been activated in response to the tornado, Oklahoma Department of Emergency Management spokeswoman Ann Lee said.

– Will Rogers World Airport reopened around at about 6 p.m. ET, spokeswoman Karen Carney said. All flights are delayed, and at least six flights have been canceled, she said.

– Lance West, a reporter for CNN affiliate KFOR, said people late Monday afternoon were pulling students from a classroom at an elementary school heavily damaged by the tornado that hit Moore. There are no immediate reports on the condition of the children.

– Congressman Tom Cole, who lives in Moore, told CNN’s Wolf Blitzer on Monday afternoon the damage he saw on TV looks as bad as a 1999 tornado that destroyed more than 1,000 houses in his hometown.

– McClain County Undersheriff Bill Shobe reported Monday afternoon there is significant damage near Newcastle, Oklahoma. Shobe went on to say there are a lot of structures with damage north of Newcastle and in the town of Tuttle. Most of the damage is parallel to Highway 37, he said.

– Moore Medical Center in Oklahoma was evacuated after it sustained damage from the tornado, a hospital spokeswoman told CNN’s Sarah Baker. All patients are being evacuated to Norman Regional Hospital and Health Plex Hospital, and residents injured in the storm are being told to go to those centers as well.

– A tornado struck Moore, Oklahoma, south of Oklahoma City, on Monday afternoon, ripping apart homes and other buildings in populated areas. The National Weather Service issued a rare tornado emergency for the Oklahoma City metropolitan area, meaning that significant and widespread damage and fatalities were likely.